1. Field of Art
This invention relates to tanks typically used for at least temporary storage and/or processing of solids, liquids, and solid/liquid slurries and sludges of varying degrees of fluidity (from relatively dry to relatively wet), often comprising wellbore drill cuttings, process waste, or other solids. With further specificity, this invention relates to such tanks comprising screw-type augers within the tank, to enable moving materials therein.
2. Related Art
Tanks having different sizes, cross sectional shapes, and internal baffles or partitions have been used for the collection, holding, and transfer of solid and liquid materials, and mixtures thereof, for many years. These mixtures form slurries and sludges of varying degrees of fluidity. More recently, tanks having some means for moving the material around inside of the tank have been used. One such means is a spiral, screw-type auger, mounted in the tank. Rotation of the auger moves materials within the tank, generally along the axis of the auger, under mechanical principles known in the art.
A typical arrangement of internal auger equipped tanks has been a tank having opposing, inclined walls which slope toward a central point at the bottom of the tank, forming in effect a trough extending at least part of the length of the tank. A single screw type auger is disposed at or near the valley of the trough. Prior art screw augers in typical use in this application have comprised a central longitudinal auger shaft, with the continuous spiral blade of the auger effectively wrapping around the auger shaft. So-called shafted augers are relatively heavy, prone to clogging, and are relatively inflexible (that is, are relatively longitudinally rigid).
The prior art tanks having screw augers therein exhibit several limitations:
I. single augers are relatively inefficient at moving materials within the tank, as only a limited portion of the cross-sectional area of the tank can be encompassed by the auger;
II. a single auger can move the materials effectively only along the axis of the auger, with relatively little ability to effectively circulate tank contents;
III. shafted screw augers arc more likely to clog with the common relatively wet and sticky slurries which such tanks contain, and are not as efficient at moving solids/liquids;
IV. shafted screw augers are relatively longitudinally stiff, and cannot readily conform to tanks not having a flat bottom; and
V. tanks with shafted screw augers exhibit a higher profile in comparison with shaftless screw augers, for a given effective cross sectional area.
In addition, the single speed drive systems of prior art screw auger-equipped tanks are relatively inflexible to accommodate differing environments, particularly different qualities in the solids, liquids, slurries, sludges, etc. that such tanks commonly hold. Prior art drive systems commonly permit rotation of the screw auger in only one rotational direction.
The present invention comprises a tank having multiple screw-type augers therein. In the presently preferred embodiment, the invention comprises a tank having opposing sides sloping inwardly toward each other from top to bottom, forming a generally V-shaped transverse cross section, typically with the apex at the bottom of the xe2x80x9cVxe2x80x9d being truncated. A plurality of shaftless screw transfer augers run along the bottom of the tank. A driver/transmission coupled to each transfer auger permits them to be operated in the same or opposite directions of rotation, and at the same or different rotational speeds, simultaneously. Materials within the tank, which may be solids, liquids, or slurries or sludges containing both, can be moved to either end of the tank by the transfer augers. An inclined lift auger, with a variable speed and rotational direction drive system, can then pick up the materials and move them out of the tank, into another tank or a desired deposit spot. Transverse baffles in the tank aid in dewatering slurries and sludges, as the slurries and sludges pass through openings in the baffles, pushed by the transfer augers. Circulation of the materials within the tank may be carried out by rotating the transfer augers in opposite directions and/or different rotational speeds.